To combine sheet metal parts firmly with each other, craft enterprises or industrial facilities such as automobile manufacturing facilities, often make use of welding robots with welding guns. During a welding operation, the welding gun presses two or more sheet metal parts together from two opposite sides, respectively, with an electric current flowing through spot welding electrodes provided in the welding gun arms so as to be able to weld the sheet metal parts together very precisely. The closing pressure of a spot welding gun during the operation can be up to 3 to 8 kN. After approximately 100 to 300 welding operations, the spot welding electrodes are worn-out to such an extent or covered with welding leftovers that any reliable welding might no longer be possible.
To enable the spot welding electrode tips to resume their original shape, said tips are dressed or finished by means of an electrode milling cutter (or tip dresser). For overhauling the worn-out spot welding electrodes consisting of a relatively soft copper it will mostly suffice to remove less than 0.1 mm of the material from the spot welding electrode tips.
Welding electrodes usually comprise exchangeable caps. However, they may also be made of one piece without such caps. The statements following below equally refer to both cases, as dressing of spot welding electrodes can be done for one-piece electrodes just as well as for electrodes having caps.
Dressing a spot welding electrode tip can be done several times (after approximately 100 to 300 welding operations, respectively). To obtain milling results of a consistently high quality, it may be advantageous to have the milling head of the milling cutter positioned as exactly as possible relative to the spot welding electrode tip for each milling operation. Optimum milling performance can be obtained when the axis of rotation of the milling cutter more or less coincides with the axis of symmetry of the spot welding electrode.
However, in practice such coincidence can only hardly be achieved, especially when the milling cutter is a hand-held milling cutter which is guided manually towards the spot welding electrode tip. During the milling operation it may happen that the milling cutter slide-slips from the spot welding electrode tip or slips out of position, or that the milling head is put onto the spot welding electrode tip in slightly inclined manner which means that, in both cases, the axis of rotation of the milling head and the axis of symmetry of the spot welding electrode coincide in a just insufficient manner.
Accordingly, it is the object of the invention described below to provide a device and a hand-held milling cutter used for dressing spot welding electrodes in such a manner that results of a consistently high quality can be achieved.